Generally, a crawler belt of a crawler-type work machine such as a bulldozer or a hydraulic excavator is formed by connecting a plurality of assemblies for a crawler belt in a loop. The crawler belt assembly has a pair of connecting links and a track shoe that is fixed to the connecting link pair. The connecting link pair includes a parallel pair of track shoe connecting links. The crawler belt is wound around a drive wheel and an idler wheel that are arranged in a body frame of the crawler-type work machine with a predetermined distance therebetween. A plurality of carrier rollers and track rollers are supported to the body frame between the drive wheel and the idler wheel. Each of the crawler belt assemblies is engaged to a sprocket of the drive wheel, and when the drive wheel is rotated in this state, the crawler belt is moved while being supported by the carrier rollers and the track rollers.
A crawler belt assembly, for example, disclosed in Patent Document 1, has been conventionally known. In the crawler belt assembly disclosed in the document, a track shoe is fixed to a pair of connecting links. A support shaft is fixed to end portions at one end of a pair of track shoe connecting links, which form the connecting link pair, and a sleeve is fixed to the other end portions. The support shaft is rotatably inserted through the sleeve of an adjacent crawler belt assembly. Accordingly, a plurality of crawler belt assemblies are connected to each other to form a loop of a crawler belt.
In the above-described crawler belt, the sleeve functions as a bearing member that rotatably connects the adjacent crawler belt assemblies to each other and also functions as a power transmission member that receives power transmitted from a sprocket by being engaged with the drive wheel. However, since the sleeve is fixed to the connecting link pair in the related art crawler belt assembly, the sleeve receives high bearing pressure in a specific portion and slidingly contacts a tooth surface of the sprocket when the work machine moves backward. Therefore, the sleeve of each crawler belt assembly may be unevenly worn at a relatively early stage. When this happens, the support shaft of the sleeve that is fixed to the support shaft is forcibly moved with respect to the support shaft so as to be turned over (this operation is referred to as bushing turn). However, the turning operation is troublesome and increases the running cost.
To solve such a problem, for example, a crawler belt assembly disclosed in Patent Document 2 has been proposed. In the crawler belt assembly, the sleeve provided between the track shoe connecting links is divided into three portions in an axial direction of the sleeve. The two end portions of the sleeve is fixed to shaft holes formed in end portions of the track shoe connecting links and a middle portion of the sleeve is externally fitted to the support shaft of an adjacent crawler belt assembly so as to be rotatable. Accordingly, relative sliding of the sprocket and the sleeve is allowed when the sleeve is engaged to the teeth of the sprocket. This prevents the wearing of the sleeve at the early stage.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-249973    Patent Document 2: Japanese National Phase Laid-open Patent Publication No. 6-504747